Replacement of a diseased or malfunctioning cardiac valve requires accurate sizing of the valve annulus. After the diseased or malfunctioning cardiac valve has been removed, the surgeon measures the patient's valve annulus to determine the appropriate replacement valve size.
A conventional system for measuring a patient's valve annulus includes a number of varying size discs, which can be removably or fixedly attached to a rod. The size of each of the discs corresponds to an available valve size. The surgeon inserts the disc into the patient's valve annulus and checks the fit of the disc within the valve annulus. If the surgeon is not satisfied with the fit, the surgeon removes the disc from the body and inserts a new disc into the valve annulus. The size of a patient's native heart valve annulus is determined by inserting sizers of various diameters until the surgeon determines which one feels correct. This is a time-consuming method since for each valve size the surgeon inserts, the surgeon must remove one of the discs and try another one. This procedure increases the overall surgery time which increases the risk to the patient and also increases the cost of the procedure. Further, the determination of the appropriate size is based on the feeling of the surgeon rather than any mechanical feature. This determination based on the feeling of the surgeon may not be accurate. Thus there is a need for a sizer that is accurate in determining the size of the annulus of a valve.
Alternatively, a heart valve sizer may be used which is introduced into the patient only once, and the same sizer is capable of gauging a number of appropriate valve sizes. However, these sizers are dimensionally the same as the valves they represent. Due to size constraints, insertion of the heart valve sizers may be a hindrance for certain procedures, especially for minimally invasive surgical incisions such as thoracotomies. With minimally invasive surgical (MIS) type procedures performed through small surgical incisions, the surgeon may not have a good approach angle to the native annulus, thus hindering an accurate tactile feedback to the surgeon when the sizer is in place.
Additionally, it is essential for the replacement heart valve to be of the right fit. In determining the optimal replacement device for a diseased heart valve, a surgeon generally exerts some level of force to determine a tight fit size. Each surgeon may have a different definition of a tight fit and what is the optimal force that may be exerted. Also, excessive force if applied may result in inaccurate sizing of the annulus, or even tissue damage. Also, traditional valves involve parachuting the valve down to the annulus with 12 to 14 sutures, and thus sizing is somewhat less sensitive. However, newer valves sometimes employ only three or in some cases no sutures making sizing accuracy more challenging. It is more difficult to avoid paravalvular leaks and risk of embolization if three or no sutures are used and there is a sizing mistake.
Given the above limitations, it is desirable to have a single, one-size-fits-all sizer which could be used to quickly and accurately determine the appropriate valve size for a patient's heart through a minimal sized incision. It is desirable to have a sizer that does not rely entirely on the surgeon's feel, but on a mechanism that consistently and more accurately determines the patient's annulus size.